In recent years, it has been expected to use photocatalyst particles for purifying polluted water and treating water containing organic pollutants. In order to ease solid-liquid separation of the photocatalyst particles dispersed in water, it has been proposed to use a photocatalyst in which titanium dioxide particles are immobilized on support particles having a larger particle diameter with a binder such as a binding agent (see Patent Literature 1, for example). In addition, there has been proposed a technique using a photocatalyst obtained by coating support particles with titanium dioxide by a coating process such as a sol gel process (see Patent Literature 2, for example).